One important thing to sort out before you make a decision is to determine whether that catalytic converter is really bad. It is surprisingly common for mechanics to mistakenly condemn a catalytic converter; when the problem really is a bad oxygen sensor that is triggering the "converter efficiency" code. Unless the converter has a hole in it, or is rattling or leaking; if you can stand behind the tailpipe and feel a blast of sound and exhaust pressure when someone in the car steps hard on the gas pedal; I seriously doubt that the converter is bad.
The question of whether you'll get ripped off on a trade in depends on the dealer, and maybe what the sales manager there ate for breakfast. The other side of the trade in picture is that they inflate the asking price of the car they want to sell you; in order to make up for the money they offer you for your car.
Considering the strong reputation of Camrys; I would personally avoid the potential hassles of dealerships and sell the car privately; and then buy a good car from a private party (only after having it thoroughly inspected and evaluated by a qualified, trustworthy, independent mechanic). That way; you will not be limited to buying only what the dealer has in stock. I would only trade in a car if there was something about it which made it difficult or impossible to sell at a fair price. And your car doesn't sound that way to me.